Interparticle distance (ID) is generally used for spatial evaluation on the dispersion of nanofillers in polymer nanocomposites (PNCs) in order to gain in-depth insight into fundamental understanding of reinforcement and structure-property correlation. However, currently available methods mainly rely on two-dimensional observation technologies or simulation methods. Herein, using layered double hydroxides (LDHs) in low-density polyethylene (LDPE) as a model matrix, we developed a novel spatial ID determination method through a post labeling fluorescent imaging technique. The spatial ID of LDH nanofillers was achieved by a MATLAB program based on the 3D coordinates of LDH nanofillers in PNCs. The spatial ID data indicated the varied dispersion states of LDH nanofillers from "random", "even", to "clustered" in PNCs. More importantly, the so-called exceptional performances of PNCs at high loading of LDH nanofillers can be reasonably explained in combination with the mechanical studies. This proposed approach could undoubtedly provide valuable information in elucidating the structure-property correlation in PNCs. We believe that this work would be a guide to design advanced PNC materials.